1. Technical Field
The present disclosure relates to systems for providing energy to biological tissue and, more particularly, to an apparatus that utilizes square waves to deliver energy to biological tissue.
2. Background of the Related Art
Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator.
Ablation is most commonly a monopolar procedure that is particularly useful in the field of cancer treatment, where one or more RF ablation needle electrodes (usually having elongated cylindrical geometry) are inserted into a living body and placed in the tumor region of an affected organ. A typical form of such needle electrodes incorporates an insulated sheath from which an exposed (uninsulated) tip extends. When RF energy is provided between the return electrode and the inserted ablation electrode, RF current flows from the needle electrode through the body. Typically, the current density is very high near the tip of the needle electrode, which tends to heat and destroy surrounding issue.
In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned immediately adjacent the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact with body tissue with either of the separated electrodes does not cause current to flow.
Typically, sinusoidal waveforms are used to deliver energy for a desired tissue effect in electrosurgical and vessel sealing applications. Creating sinusoidal waveforms requires the use of low harmonic content linear drive or resonant switching amplifier topologies. However, linear drive electronics, which use linear components such as resistors, capacitors and inductors, tend to be inefficient due to the power loss caused by such linear components. With regard to resonant amplifier topologies, such topologies require large resonant components to shape the output waveform.
Further, in order to achieve excellent tissue sealing performance, it is important to monitor the impedance of the tissue to which energy is being applied. The impedance is calculated by measuring the root mean square (RMS) voltage and current of the radio frequency (RF) energy output to calculate the tissue impedance. However, with sinusoidal waveforms, complicated sensing hardware and/or signal processing is required to accurately calculate RMS voltage and/or current. Further, sinusoidal waveforms tend to have a peak voltage that 1.414 times the RMS voltage of the waveform. The higher peak voltage may have a negative impact on certain tissue treatments.